lundurine-a and indoline

A total synthesis of (±)-lundurines A and B is described. These natural products have a unique hexacyclic skeleton which includes a cyclopropane-fused indoline. A stereospecific construction of the pentasubstituted cyclopropane core was achieved, by radical cyclization using SmI2, with perfect stereoselectivity. Cyclizations to give seven- and five-membered heterocycles, under palladium and ruthenium catalysis, respectively, accomplished the total syntheses. The late-stage construction of the F ring by ring-closing metathesis enabled access to the title compounds from a spiroindoline intermediate which is a common structure of other kopsia alkaloids.

Topics: Alkaloids; Apocynaceae; Catalysis; Cyclization; Indoles; Palladium; Polycyclic Compounds; Ruthenium; Stereoisomerism